Photomask blank manufacturing method, photomask blank, photomask, and pattern transfer method

ABSTRACT

The method for manufacturing a photomask blank according to the present invention, when manufacturing a photomask blank having at least one functional layer on a transparent substrate, in a step of film-formation of such a functional film where the functional film includes a chromium-containing element and an a metallic element that is capable of bringing a mixture of the metallic element and the chromium into a liquid phase at a temperature of 400° C. or lower, a chromium target (target A) and a target (target B) mainly containing at least one kind of the metallic element are simultaneously sputtered (co-sputtered). The present invention provides a technique for manufacturing a functional film having a small variation in its characteristics such as optical density and a low detect, and showing a high etching rate.

TECHNICAL FIELD

The present invention relates to a photomask blank and a method formanufacturing the same, a photomask obtained from the photomask blank,and a method for pattern transfer using the photomask.

BACKGROUND ART

In the field of semiconductor technology, research and development forfurther refinement of patterns have been progressed. In recent years,particularly, with high integration of a large scale integrationcircuit, refinement of circuit patterns, refinement of wiring patterns,or refinement of contact-hole patterns for wiring between layers forminga cell has been progressed. Thus, a request for microfabricationtechnology has been increased.

In connection with this, even in the field of technology for photomaskproduction to be used in the process for photolithography inmicrofabrication, a technique for forming fine and correct circuitpatterns (mask patterns) has begun to be demanded.

Generally, reduction projection is performed when forming a pattern on asemiconductor substrate by photolithographic technique. The size ofpattern formed on the photomask is therefore approximately four timeslarger than the side of pattern formed on the semiconductor substrate.However, this does not mean that the desired precision of patternsformed on the photomask is smaller than the patterns formed on thesemiconductor substrate. Rather, the precision of patterns formed on thephotomask as a master is desired to be higher than actual patternsobtained after exposure.

In today's photolithography technical field, the size of a circuitpattern to be drawn is considerably smaller than the wavelength of lightto be used for exposure. Thus, in the case of forming a photomaskpattern with a just four-time enlarged circuit pattern, lightinterference or the like, which is generated under exposure, results inun-transferred original shape on a resist film of a semiconductorsubstrate.

In some cases, therefore, a pattern formed on the photomask is made morecomplicated than an actual circuit pattern to reduce an effect of theabove light interference or the like. The shape of such a pattern maybe, for example, an actual circuit pattern subjected to opticalproximity correction (OPC).

Hence, along with a decrease in size of a circuit pattern, a higherprecision processing technique has been also desired in a lithographictechnique for forming photomask patterns. Although lithographyperformance may be expressed in limiting resolution, a pattern formed ona photomask as a master desires higher precision than an actual patternformed after exposure as described above. Thus, limiting resolutionrequired for formation of a photomask pattern is almost equal to orhigher than one required in lithography for forming a pattern on asemiconductor base.

Incidentally, when forming a photomask pattern, a resist film is usuallyformed on the surface of the photomask blank formed of a light-shieldingfilm on a transparent substrate, and a pattern is then drawn (exposed)on the resist film by an electron beam. Subsequently, after obtaining aresist pattern after developing the exposed resist film, alight-shielding film is etched by using this resist pattern as a mask toobtain a light-shielding (film) pattern. The light-shielding (film)pattern thus obtained is served as a photomask pattern.

In this case, the above-mentioned resist film should be thinneddepending on the degree of fineness of the light-shielding pattern. Thisis because, when forming a fine light-shielding pattern while keepingthe thickness of the resist film, the ratio (aspect ratio) of thethickness of the resist film to the size of the light-shielding patternbecomes large and causes troubles of failed pattern transfer, fallingdown or peeling off of the resist pattern, or the like due todeterioration of the shape of the resist pattern.

As a material of the light-shielding film disposed on the transparentsubstrate, many kinds of materials have so far been proposed. Amongthem, however, a chromium compound has been practically used because ofmany know-how on etching, for example.

Dry etching of a chromium-containing material film is generallyperformed by chlorine-containing dry etching. In many cases, however,chlorine-containing dry etching has a certain level of ability to etchan organic layer. Thus, in the case that a resist pattern is formed on athin resist film and then used as a mask to etch a light-shielding film,the resist pattern is also etched too much to ignore bychlorine-containing dry etching. As a result, the proper resist pattern,which should be transferred to a light-shield film, cannot be correctlytransferred to the light-shielding film.

In order to avoid such inconvenience, a resist material having excellentetching resistance has been requested. However, such a resist materialhas not been known yet. For this reason, to obtain a light-shielding(film) pattern having high resolution property, a light-shielding filmmaterial having higher processing accuracy is required.

For a light-shielding film having higher processing accuracy as comparedwith a conventional material, there is a report of an attempt toincrease the etching rate of a light-shielding film by allowing achromium compound to contain only a certain amount of a light element.

For example, patent Literature 1 (WO 2007/74806 A) discloses a techniquethat uses a material mainly containing chromium (Cr) and nitrogen (N)and having an X-ray diffraction peak of substantially CrN (200) as alight-shielding film material to suppress a decrease in thickness of aresist film by increasing the dry etching rate of the light-shieldingfilm.

Furthermore, Patent Literature 2 (JP 2007-33470 A) discloses theinvention of a photomask blank where its composition, film thickness,and a laminated structure are suitably designed to obtain desiredtransmittance T and reflectance R while trying to increases adry-etching rate by making the composition of a chromium-containingcompound of the light-shielding film rich in light element and low inchromium composition as compared with the composition of theconventional film.

CITATION LIST Patent Literatures

-   Patent Literature 1: WO 2007/74806 A-   Patent Literature 2: JP 2007-33470 A-   Patent Literature 3: JP 7-140635 A-   Patent Literature 4: JP 2007-241060 A-   Patent Literature 5: JP 2007-241065 A

SUMMARY OF THE INVENTION Technical Problem

When using a light-shielding film material in which a light element isadded to a chromium-containing compound, the light-shielding film shouldnot only ensure its improved etching rate but also ensure predeterminedoptical containing characteristics because the light-shielding film isalso served as an optical film. However, the flexibility of the filmdesign enough to simultaneously satisfy both demands is not always high.

Even in the case of using a material in which a light element is addedto a chromium-based compound not as a light-shielding film material butas a film material for forming a hard mask, a range of amount of thelight element which can be added is naturally limited to ensure thefunctional aspect of the chromium-based compound. Thus, the flexibilityof a film design is not always high.

In other words, from the viewpoint of improving the etching rate of afilm while ensuring predetermined optical characteristics, aconventional technique, such as addition of a light element, haslimitations. Therefore, another approach using another techniquedifferent from such a conventional technique has been desired. Inconsideration of such a background, the present inventors have studiedthe use of a chromium-containing material as an optical film, where thematerial is added with a metal element that is capable of, when mixedwith chromium, bringing the mixture into a liquid phase at a temperatureof 400° C. or lower.

When the optical film made of such a chromium-containing material isformed by sputtering, a content ratio between the chromium element andthe above additive metal element in the optical film should be broughtinto a suitable range to obtain desired optical characteristics.Typically, in this case, a chromium target that contains the abovemetallic element only in small amount is prepared and then used insputtering film-formation. However, adoption of such a film-formingprocess may cause problems as described below.

Even though a typical chromium target to be used in sputteringfilm-formation is produced by sintering, the above additive metallicelement is capable of, when mixed with chromium, bringing the mixtureinto a liquid phase at a temperature of 400° C. or lower. Thus, when theabove metallic element is added to the chromium target in amount enoughto give the desired optical characteristic values of a film and increasethe etching rate, the sintering temperature has to be inevitably set to400° C. or lower. However, even if the sintering is performed at such acomparatively low temperature, the sintering may proceed insufficiently.As a result, the target may have insufficient sintered density or mayhave insufficient composition distribution.

If a film is formed using a target having insufficient sintered density,foreign matter generated from the target may cause a defect in the film.Furthermore, when a film is formed using a target having unevenlydistributed composition, the composition distribution in the surface ofthe film or between the surfaces of the respective films may also becomeuneven. As a result, the resulting film may cause a problem that itcannot sufficiently exert its function as an optical film.

The present invention has been made in order to solve these problems andan object thereof is to provide a technique for manufacturing ahigh-quality optical film (functional film) showing a small variation inits characteristics such as optical density and having a low detect aswell as having a high etching rate, a method for manufacturing aphotomask blank using such a technique, and so on.

Solution to Problem

To solve the aforementioned problems, a method for manufacturing aphotomask blank according to the present invention is one formanufacturing a photomask blank having at least one functional film on atransparent substrate, where the functional film is made of achromium-containing material including a chromium element and a metallicelement that is capable of bringing a mixture of the metallic elementand the chromium into a liquid phase at a temperature of 400° C. orlower; and, in a step of forming the functional film, a chromium target(target A) and a target (target B) mainly containing at least one kindof the metallic element are simultaneously sputtered (co-sputtered).

Alternatively, in the step of forming the functional film, it may beconfigured to use at least one of the target A and the target B two ormore.

Preferably, S_(B)<S_(A) is given when the total area of the target A isS_(A) and the total area of the target B is S_(B).

Preferably, in this case, a ratio (S_(B)/S_(A)) between the totalsurface are S_(A) and the total surface area S_(B) is set to 0.7 orlower.

Preferably, furthermore, a ratio (S_(B)/S_(A)) between the total surfaceare S_(A) and the total surface area S_(B) is set to 0.01 or higher.

The functional film includes at least one of a light-shielding film, ananti-reflection film, an etching mask film, and an etching stopper film.

Alternatively, the functional film includes any of a light-shieldingfilm or an anti-reflection film.

Alternatively, the functional film is a light-shielding film.

The photomask blank according to the present invention is a photomaskblank manufactured by the above method, where a content ratio([Me]/[Cr]) between chromium element (Cr) and a metallic element (Me)that is capable of bringing a mixture of the metallic element and thechromium into a liquid phase at a temperature of 400° C. or lower is 0.7or lower in terms of atomic ratio in the functional film.

In addition, the photomask according to the present invention is aphotomask obtained by forming a pattern on the above photomask blank.

In the method for pattern transfer according to the present invention,furthermore, exposure is performed using the photomask and the patternis then transferred on a photoresist.

Advantageous Effects of Invention

According to the present invention, in a step of forming a functionalfilm where the functional film is formed using a chromium-containingmaterial including a chromium element and a metallic element that iscapable of bringing a mixture of the metallic element and the chromiuminto a liquid phase at a temperature of 400° C. or lower, a chromiumtarget (target A) having a surface area of S_(A) and a target (target B)mainly containing one kind of the above metal element as a maincomponent and having a surface of S_(A) (<S_(A)) are simultaneouslysputtered (co-sputtered). Therefore, generation of foreign matter fromthe target is sufficiently suppressed, and a functional film havingstable quality can be obtained.

Such a functional film has a small variation in its characteristics suchas optical density and a low detect, and also shows a high etching rate.Therefore, it is possible to increase an etching rate while ensuringpredetermined optical characteristics.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating an exemplary configuration of anapparatus to be used in manufacture of a photomask blank by the methodaccording to the present invention.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments for carrying out the present invention will bedescribed with reference to the drawing. However, the present inventionis not limited to these embodiments.

Prior to the description of the present invention, the present inventorswill describe the story of why the present inventors have completed thepresent invention.

As described above, the present inventors have studied the use of achromium-containing material as an optical film, where the material isadded with a metal element that is capable of, when mixed with chromium,bringing the mixture into a liquid phase at a temperature of 400° C. orlower.

During this process, the present inventors have recognized the followingmatters as problems to be solved: When the above metallic element isadded to the chromium target in amount enough to give the desiredoptical characteristic values of a film and increase the etching rate,the sintering temperature has to be inevitably set to 400° C. or lower;and as a result, the target may have insufficient sintered density ormay have insufficient composition distribution.

To solve the problems, it is conceived that an effective method is onefor forming a functional film by preparing a target (target B)containing at least one kind of the above metallic element as a maincomponent in addition to a chromium target (target A), andsimultaneously sputtering (co-sputtering) them to form a functionalfilm.

Based on the above finding, the method for manufacturing a photomaskblank according to the present invention, when manufacturing a photomaskblank having at least one functional layer on a transparent substrate,in a step of film-formation of such a functional film where thefunctional film includes a chromium-containing element and an a metallicelement that is capable of bringing a mixture of the metallic elementand the chromium into a liquid phase at a temperature of 400° C. orlower, a chromium target (target A) and a target (target B) mainlycontaining at least one kind of the metallic element are simultaneouslysputtered (co-sputtered).

The method for manufacturing the photomask blank according to thepresent invention may be provided as an embodiment in which each of theabove target A and the above target B is used one at a time, or may beprovided as an embodiment in which one of them is used two or more at atime, or may be provided as an embodiment in which each of them is usedtwo or more at a time.

However, even in the case of carrying out the above co-sputtering,chromium fine particles flying from the chromium target (target A)attaches the surface of the metal element-containing target (target B).The chromium fine particles may cause another problem in that theparticles act as a nucleus to generate a nodule (agglomerated materialformed in the target B) causing the generation of a defect in thefunctional film in the process of film-formation.

Such chromium particles are removable if the sputtering power density(W/cm²) supplied to the target B is increased to a certain degree.However, the content of the above metallic element in the film, which isdefined to obtain a functional film having desired opticalcharacteristics, is not so high. Thus, the sputtering power (W) suppliedto the target B should be set to a comparatively low value. In otherwords, obtaining the functional film having desired opticalcharacteristics and preventing the generation of a defect in thefunctional film by removing chromium fine particles may be contradictingeach other from a viewpoint of the supply of sputtering power to thetarget B.

Therefore, regardless of the sputtering power density (W/cm²) suppliedto the target A, it has been desired to suitably control the sputteringpower density (W/cm²) supplied to the target B.

However, when the supplied power density (W/cm²) is lowered in order toset the sputtering power (W) supplied to the target B to a comparativelylow value, discharge itself may become unstable. To solve this problem,what is necessary is to realize the supplied power density (W/cm²) thatleads to a stable discharge even when the sputtering power (W) suppliedto the target B is set to a comparatively low value.

In the present invention, therefore, to achieve a supplied power density(W/cm²) that does not lead to an unstable discharge even when thesputtering power (W) supplied to the target B is set to a comparativelylow value, the suitable power density (W/cm²) supplied to the target Bis achieved by making the total surface area of the target B small. Inother words, the total surface area (S_(A)) of the target A and thetotal surface area (S_(B)) of the target B are made different from eachother, S_(B)<S_(A), and electric power is supplied to both the targets Aand B with their respective optimal power flux densities. Even if thesputtering power (W) supplied to the target B is set to a comparativelylow value, the supplied power density (W/cm²) in the range that does notlead to an unstable discharge is achieved.

A ratio (S_(B)/S_(A)) between such total surface areas S_(A) and S_(B)is preferably set to 0.7 or lower and preferably to 0.01 or higher.

The functional film to be formed by such a method includes, for example,at least one of a light-shielding film, an anti-reflection film, anetching mask film, and an etching stopper film, which is formed on aphotomask blank. Alternatively, the above functional film includes oneof a light-shielding film or an anti-reflection film. Alternatively, theabove functional film is a light-shielding film.

Such a method can provide a photomask blank where a content ratio([Me]/[Cr]) between a chromium element (Cr) and a metallic element (Me)capable of bringing a mixture of the metallic element and the chromiuminto a liquid phase at a temperature of 400° C. or lower is 0.7 or lowerin terms of atomic ratio.

Exposure is performed using a photomask obtained by forming a pattern onsuch a photomask blank to transfer the pattern on the photoresist.

FIG. 1 is a diagram illustrating an exemplary configuration of anapparatus used in manufacture of a photomask blank according to theabove method.

[Sputtering Film-Formation System]

In a chamber 101 used in a sputtering film-formation 100 illustrated inthis FIGURE, one chromium target (target A: 102A) and one target (targetB: 102B) mainly containing a metallic element that is capable ofbringing a mixture of the metallic element and the chromium into aliquid phase at a temperature of 400° C. or lower are arranged. Electricpower is applied to the target 102A and the target 102B from the powersources 103A and 103B, respectively. In this FIGURE, furthermore, onetarget A and one target B are illustrated. However, at least one kind ofthese targets may be provided two or more.

A transparent substrate 104, which is a film-formation substrate for afunctional film, is held on a rotatable holder 105 in a state that afilm-forming surface thereof faces the surface of the target. An exampleof such a transparent substrate 104 may be a substrate made of quartz,CaF₂, or the like and transparent to exposure light. In the chamber 101,a gas introducing line 106 for introduction of sputtering gas and anexhaust line 107.

The surface area S_(B) of the target B is designed to be smaller thanthe surface area S_(A) of the target A. If there are two or more targetsA, the above S_(A) represents the sum of the total surface areas of therespective targets A. Similarly, if there are two or more targets B, theabove S_(B) represents the sum of the total surface areas of therespective targets B.

By setting the total surface area of the target B to S_(B)<S_(A), evenin the case that there is a need of lowering electric power (W) suppliedto the target B, it becomes possible to generate a stable discharge andto previously prevent the target B from generating a nodule

A ratio (S_(B)/S_(A)) between the total surface areas is preferably setto 0.7 or lower, more preferably to 0.01 or higher. When the totalsurface area is set to a value higher than 0.7, the discharge of thetarget B may become unstable under the conditions for allowing thetarget A to be stably discharged. On the other hand, when the totalsurface area is set to a value smaller than 0.01, the discharge of thetarget B may become excess under the conditions for allowing the targetA to be stably discharged. As a result, a disadvantage such as melt of abonding material can be occurred.

[Sputtering Gas]

Sputtering gas is suitably selected according to the composition of thefunctional film. The inert gas for sputtering is preferably inert gas ofneon, argon, krypton, or the like. More preferably, at least one kind ofreactive gas selected from oxygen-containing gas, nitrogen-containinggas, and carbon-containing gas is introduced together with the aboveinert gas. When using such reactive gas as sputtering gas, thefilm-formation is performed by reactive co-sputtering.

Examples of the above oxygen-containing gas include CO₂, NO, and O₂.Examples of the above nitrogen-containing gas include NO, NO₂, and N₂.Example of the above carbon-containing gas include CH₄, CO₂, and CO. Thekind of reactive gas to be used depends on the composition of thefunctional film of interest.

For example, inert gas such as argon as sputtering gas when a lightelement is not included in a chromium-containing material including achromium element and a metallic element that is capable of bringing amixture of the metallic element and the chromium into a liquid phase ata temperature of 400° C. or lower. In the case of film formation of afunctional film containing a light element, reactive sputtering may beperformed in one or more kinds of reactive gas, such as nitrogen gas,nitrogen oxide gas, oxygen gas, or carbon oxide gas, or mixture gas ofany of those reactive gas and inert gas such as argon (see, for example,JP 7-140635 A (Patent Literature 3)).

The flow rate of sputtering gas is adjusted suitably. The gas flow ratemay be constant in the process of film-formation. Alternatively, the gasflow rate may be changed according to the target composition when thereis a need of changing the amount of oxygen or the amount of nitrogen ina thickness direction.

Examples of the sputtering method, which can be employed in the presentinvention, may include, but not specifically limited to, DC sputtering,RF sputtering, RF sputtering, and magnetron sputtering. Furthermore, inthe process of sputtering, when the transparent substrate is configuredso that a target sputtering surface faces the target is rotated, it isexpected to exert an effect of increasing an inner surface uniformity ofthe characteristics of the functional film obtained.

[Target B]

The target B used in the film-formation of a functional film containingthese metallic elements is a target mainly containing the above metallicelement, and examples of such a target includes as an indium target, atin target, and an indium bismuth target. Furthermore, a light elementmay be included in any of these targets. The target may be, for example,a target made of indium and a light element, such as a target made ofindium and oxygen or a target made of indium and oxygen; a target madeof tin and a light element such as a target made of tin and oxygen or atarget made of tin and nitrogen; or a target made of bismuth and a lightelement, such as a target made of bismuth and nitrogen or a target madeof bismuth and oxygen. Among these targets, the most preferable one isthe target made of tin or made of both tin and oxygen.

The light element contained in the target may be carbon. The lightelement contained in the target may include one or more kind ofnitrogen, oxygen, and carbon.

The content of the above metallic element (Me) that is capable ofbringing a mixture of the metallic element and the chromium into aliquid phase at a temperature of 400° C. or lower (the composition ratioof Me and an element other than Me: [Me]/[element other than Me]) ispreferably 0.5 or higher in atomic ratio. This atomic ratio ispreferably 0.7 or higher, further preferably 1.00 or higher.

There is no upper limit of the value of this composition ratio. If thereare two or more kinds of metallic element capable of bringing a mixtureof the metallic element and the chromium into a liquid phase at atemperature of 400° C. or lower, the target B is formed such that totalamount of these metallic elements satisfy the above composition ratio.

Two or more kinds of the target B having different compositions may beused. For example, an indium target and a tin target may be usedtogether, or a target made of indium and a target made of tin and oxygenmay be used together. Thus, by making the target B as a plurality oftargets, the composition distribution of the functional film in athickness direction can be designed in various ways.

[Electric Power Applied to Target]

Power density (W/cm²) supplied to each of the target A and the target Bis individually controllable, and each of the target A and the target Bcan be set to a value that leads to a stable discharge. In general, thepower density supplied to the chromium target (target A) is 0.5 W/cm² orhigher and 20.0 W/cm² or lower. Similarly, the power density supplied tothe target (target B) mainly containing at least one metallic elementcapable of bringing a mixture of the metallic element and the chromiuminto a liquid phase at a temperature of 400° C. or lower is 5 W/cm² orhigher and 20.0 W/cm² or lower.

When the power density supplied to the target goes out of the above ragedownwardly, the discharge of the target tends to be instable. Therefore,the number of defects in the functional film may occur. On the otherhand, the power density supplied to the target goes out of the rangeupwardly, the discharge of the target becomes excess. Thus,disadvantages such as the generation of abnormal discharge and the meltof a bonding material fixing the target on a backing plate tend tooccur. As a result, a decrease in quality of the functional film mayoccur.

[Functional Film]

The functional film prepared as descried above is made of achromium-containing material including a chromium element and a metallicelement that is capable of bringing a mixture of the metallic elementand the chromium into a liquid phase at a temperature of 400° C. orlower. It is preferred that a content ratio ([Me]/[Cr]) between achromium element (Cr) and a metallic element (Me) capable of bringing amixture of the metallic element and the chromium into a liquid phase ata temperature of 400° C. or lower be 0.7 or lower. A more preferableatomic ratio is 0.4 or lower, and a further preferable atomic ratio is0.3. Alternatively, the atomic ratio may be 0.2 or lower. The lowerlimit of the atomic ratio is one that allows an etching rate at the timeof dry-etching the functional film to be substantially equal to that ofthe conventional functional film, and the content ratio is the lowerlimit, generally 0.01 or higher.

The functional film formed on the transparent substrate is not limitedto a single layer structure. Alternatively, it may be a functional filmprepared by stacking a plurality of layers.

Furthermore, the functional film is not limited to include a single kindof the metallic element capable of bringing a mixture of the metallicelement and the chromium into a liquid phase at a temperature of 400° C.or lower. Alternatively, the functional element may include two or morekinds of the above metallic element.

Examples of such a metallic element include indium, tin, bismuth,thallium, lithium, sodium, potassium, and mercury. Among them, indium(T_(L)=157° C.), tin (T_(L)=232° C.), and bismuth (T_(L)=271° C.) arepreferable. In particular, indium (T_(L)=157° C.) and tin (T_(L)=232°C.) are preferable.

In the functional film made of a chromium-containing material accordingto the present invention, such a chromium-containing material is onethat contains a chromium element and a metallic element, where themetallic element is capable of bringing a mixture of the metallicelement and the chromium into a liquid phase at a temperature of 400° C.or lower. Examples of such a chromium-containing material include achromium metal and chromium compounds such as chromium oxide, chromiumnitride, chromium carbide, chromium oxynitride, chromium oxide carbide,chromium nitride carbide, and chromium oxide nitride carbide. Amongthem, chromium nitride, chromium oxynitride, and chromium oxide nitridecarbide are particularly preferred.

A film having the same characteristics as those of the conventionalchromium-containing material film and having an improved dry-etchingrate can be obtained by using the functional film made of achromium-containing material according to the present invention as alight-shielding film (see, Patent Literatures 1 and 2), a hard mask film(Patent Literature 4: JP 2007-241060 A), an etching stopper (PatentLiterature 5: JP 2007-241065 A), or the like. As a result, thepatterning precision of an inorganic material film can be improvedwithout any specific design change of the chromium-containing materialfilm.

[Light-Shielding Film]

In the case of using the functional film of the present invention as alight-shielding film, the film may be one made of a chromium-containingmaterial including a chromium element and a metallic element that iscapable of bringing a mixture of the metallic element and the chromiuminto a liquid phase at a temperature of 400° C. or lower. Alternatively,the film may be preferably made of an oxide, nitride, oxynitride,oxycarbonitride, or oxycarbonitride of chromium and the above metallicelement. In particular, a metal-rich composition film (unsaturated metalcompound film) in which the contents of oxygen, nitrogen, and carbon aresmaller than their stoichiometric amounts is preferred.

As described above, examples of the above metallic element includeindium, tin, bismuth, thallium, lithium, sodium, potassium, and mercury.Among them, indium (T_(L)=157° C.), tin (T_(L)=232° C.), and bismuth(T_(L)=271° C.) are preferable. In particular, indium (T_(L)=157° C.)and tin (T_(L)=232° C.) are preferable.

According to the investigation of the present inventors, the content ofthe above metallic element in the light-shielding film is preferably0.01 atomic % or higher. Such a light-shielding film has a significantimprovement in etching rate under general chlorine-containing dryetching conditions.

For the purpose of improving the etching rate of a light-shielding filmat the time of chlorine-containing dry etching under general conditions,the content of the above metallic element in a specific region in athickness direction may be 0.01 atomic % or higher. The content of themetallic element is preferably 0.5 atomic % or higher, furtherpreferably 1 atomic % or higher.

Although there is no specific upper limit of the content of the abovemetallic element, an excess content thereof leads to difficulty inobtaining desired characteristics. This value is generally 40 atomic %or lower, preferably 20 atomic % or lower.

The above metallic element does not need to be uniformly distributed inthe light-shielding film in the thickness direction (depth directionprofile) of the film, and it may have a profile having a change inconcentration in the thickness (depth) direction of the film. Forexample, when the profile is of a gradual decrease in concentration ofthe above metallic element from the substrate side to the surface sideof the light-shielding film, a good cross-sectional shape of the filmunder chromium-containing dry etching can be obtained.

The light-shielding film may be configured in any of other variousvariations. For example, the light-shielding film may be a stack of alayer made of a chromium-containing material including an a metallicelement that is capable of bringing a mixture of the metallic elementand chromium into a liquid phase at a temperature of 400° C. or lowerand a layer made of a chromium-containing material without a metallicelement.

For example, the laminated structure may be configured to have an upperlayer made of a chromium-containing material which does not contain an ametallic element that is capable of bringing a mixture of the metallicelement and the chromium into a liquid phase at a temperature of 400° C.or lower and a lower layer made of a chromium-containing materialincluding a metallic element that is capable of bringing a mixture ofthe metallic element and the chromium into a liquid phase at atemperature of 400° C. or lower. In this case, the cross-sectional shapeof the film at the time of chlorine-containing dry etching can bemaintained good by increasing only the etching rate of the lower layer(on the substrate side) in contrast to the etching rate of the upperlayer (on the surface side).

Such a laminate structure may be configured in any of other variousvariations. For example, it may have a structure in which a plurality oflayers that are respectively made of chromium-containing materials withdifferent contents of the above metallic elements. Even in the case ofsuch a laminated structure, electric power applied to each of the targetA and the target B is controlled within a range that allows the targetto be stably discharged. Sputtering of the target B can be temporarilyunrequired. In this case, there is no need of completely stopping thesupply of electric power to the target B. The electric power may besupplied as long as it does not cause unstable discharge. Therefore, thegeneration of abnormal discharge at the time of restarting the supply ofelectric power which has been temporally stopped.

In the case of a light-shielding film having a laminated structure isone in which an antireflection layer and a light-shielding layer arestacked together, it is possible to provide a variation in which onlythe antireflection layer may have a content of the above metal elementof 0.01 atomic % or higher, or only the light-insulating layer may havea content of the above metallic element is 0.01 atomic % or higher.

When using the functional film made of the chromium-containing materialof the present invention as a light-shielding film provided in aphotomask blank, just as in the case with the conventional inorganicfilm, a light element such as oxygen or nitrogen, or further carbon orhydrogen can be suitably added if needed to keep desired opticalfunctions and chemical functions.

In this case, to form a pattern of a half pitch node of 40 nm, thelight-shielding film has a film thickness of 75 nm or lower and theresist film has a film thickness of 150 nm or lower.

[Hard Mask Film]

The functional film made of a chromium-containing material including achromium element and an a metallic element that is capable of bringing amixture of the metallic element and the chromium into a liquid phase ata temperature of 400° C. or lower can be used as a hard mask film formicro-processing of a photomask blank, for example. In this case, as apreferred variation, in addition to a chromium metal film mainlycontaining at least one kind of a metallic element that is capable ofbringing a mixture of the metallic element and the chromium into aliquid phase at a temperature of 400° C. or lower as a principalcomponent, an exemplary film can be of a chromium compound containing ametallic element that is capable of bringing a mixture of the metallicelement and the chromium into a liquid phase at a temperature of 400° C.or lower and one or more kind of a light element selected from oxygen,nitrogen, and carbon.

Examples of the chromium-containing material used in such a hard maskfilm include chromium oxide, chromium nitride, chromium oxynitride,chromium oxide carbide, chromium nitride carbide, and chromiumoxynitride carbide.

Furthermore, when such a functional film made of a chromium-containingmaterial film is used as a hard mask film formed on a photomask blankused in production of a photomask for forming a resist pattern of 50 nmor lower, the film thickness is preferably 1 to 30 nm, particularlypreferably 1 to 10 nm.

[Etching Stopper Film]

When using the functional film made of a chromium-containing material ofthe present invention as an etching stopper film of a photomask blank,the same material as that of the etching mask film can be selected.

If the thickness of the etching stopper film of such a material is 1 to30 nm, any problem due to crude density dependence in processing of anetching stopper film cannot be generated. In addition, a good etchingmask effect can be obtained in processing of a film or a transparentsubstrate provided under the etching stopper film. Thus, the etchingprecision of a film or a transparent substrate provided under theetching mask film can be increased. If the thickness of an etchingstopper film is set to 2 to 20 nm, a further preferable etching maskeffect can be obtained.

[Dry Etching]

The functional film made of a chromium-containing material, which isobtained according to the present invention, can be dry-etched bychlorine gas containing oxygen in a manner similar to the conventionalchromium-containing material film that does not contain any metallicelement capable of bringing a mixture of the metallic element and thechromium into a liquid phase at a temperature of 400° C. or lower. Theetching rate of the functional film under the same conditions issignificantly high as compared with the conventional chromium-containingmaterial film.

The dry etching can be performed, for example, using gas of chlorine gasand oxygen gas at a mixture ratio (Cl₂ gas:O₂ gas) of 1:2 to 20:1 interms of volumetric flow rate, and optionally mixed with inert gas suchas helium (He).

Here, the present invention will be described in details with referenceto examples.

EXAMPLES Example

In this example, a chromium (Cr) target (target A) of 6 inches indiameter and a tin (Sn) target (target B) of 5 inches in diameter wereprepared on a quartz substrate of 152 mm on a side and 6 mm inthickness. Therefore, the ratio (S_(B)/S_(A)) of the total surface areaof the target A and the total surface area of the target B is 25/36(approximately 0.694). Different electric powers are applied to thetargets and the targets were then co-sputtered by a DC-sputtering methodto form a Sn-containing CN film of 44 nm in thickness. The compositionof the CrON film was Cr:Sn:O:N=4:1:5:2 (atomic ratio). Therefore, thecontent ratio [[Sn]/[Cr]] of Cr and Sn in the film is 0.25 in atomicratio.

The content of tin in the CrON film was adjusted by setting electricpowers applied to the chromium target and the tin target to 1000 W and400 W, respectively. Sputtering gas used was a mixed gas ofAr:O₂:N₂=5:3:6. The gas pressure in the chamber in sputtering was 0.1Pa.

Film-formation of the above CrON film was performed 10 times, and 10samples obtained were then evaluated with respect to variations inoptical density and the number of defects.

Variations in optical density were evaluated. That is, the opticaldensity of the center portion of the film was measured at a wavelengthof 193 nm, and variations between samples were then evaluated. As aresult, variations in optical density were ±0.02%.

The number of defects was evaluated on the above 10 samples. The numberof defects of 0.2 μm or more in size was counted by GM-1000 manufacturedby Hitachi Engineering Co., Ltd, followed by calculation of an averagevalue. As a result, the number of defects was 0.8/sample.

Such a functional film obtained in the present invention has a smallvariation in its characteristics such as optical density and a lowdetect, and also shows a high etching rate. Therefore, it is possible toincrease an etching rate while ensuring predetermined opticalcharacteristics.

Such a functional film can be formed by the sputtering device accordingto the present invention.

The sputtering device of the present invention includes a chromiumtarget (target A) and a target (target B) as separate film-formingtargets, where the target B mainly contains a metallic element that iscapable of bringing a mixture of the metallic element and the chromiuminto a liquid phase at a temperature of 400° C. or lower as a principalcomponent. Here, electric power is independently supplied to thefilm-forming targets, and the surface area S_(B) of the target B isdesigned smaller than the surface area S_(A) of the target A.

The sputtering device of the present invention can be designed such thatat least one of the target A and the target B is arranged more than one.

Preferably, a ratio (S_(B)/S_(A)) between the total surface area S_(B)of the target B and the total surface area S_(A) of the target A is 0.7or lower and 0.01 or higher.

Furthermore, the sputtering device of the present invention includes aholder configured to be in-plane rotatable, and it may be designed suchthat a sputtering substrate for film formation is held on the holderwhile a film-forming surface of the sputtering substrate is kept facingthe surface of the target.

INDUSTRIAL APPLICABILITY

The present invention provides a functional film having a smallvariation in its characteristics such as optical density and a lowdetect, and also showing a high etching rate. According to the presentinvention, there is provided a functional film that makes possible toincrease an etching rate while ensuring predetermined opticalcharacteristics.

REFERENCE SINS LIST

-   100 Sputtering film-formation system-   101 Chamber-   102A Target A-   102B Target B-   103A, 103B Power source-   104 Transparent Substrate-   105 Holder-   106 Gas Introducing Line-   107 Exhaust Line

1. A method for manufacturing a photomask blank having at leastfunctional film on a transparent substrate, wherein the functional filmis made of a chromium-containing material including a chromium elementand a metallic element that is capable of bringing a mixture of themetallic element and the chromium into a liquid phase at a temperatureof 400° C. or lower; and, in a step of forming the functional film, achromium target (target A) and a target (target B) mainly containing atleast one kind of the metallic element are simultaneously sputtered(co-sputtered).
 2. The method for manufacturing a photomask blankaccording to claim 1, wherein, in the step of forming the functionalfilm, at least one of the target A and the target B is used more thanone.
 3. The method for manufacturing a photomask blank according toclaim 1, wherein an expression: S_(B)<S_(A) is given when the total areaof the target A is S_(A) and the total area of the target B is S_(B). 4.The method for manufacturing a photomask blank according to claim 3,wherein a ratio (S_(B)/S_(A)) between the total surface area S_(A) andthe total surface area S_(B) is set to 0.7 or lower.
 5. The method formanufacturing a photomask blank according to claim 4, wherein, a ratio(S_(B)/S_(A)) between the total surface area S_(A) and the total surfacearea S_(B) is set to 0.01 or higher.
 6. The method for manufacturing aphotomask blank according to claim 1, wherein the functional filmincludes at least one of a light-shielding film, an anti-reflectionfilm, an etching mask film, and an etching stopper film.
 7. The methodfor manufacturing a photomask blank according to claim 1, wherein, thefunctional film includes any of a light-shielding film or ananti-reflection film.
 8. The method for manufacturing a photomask blankaccording to claim 1, wherein, the functional film is a light-shieldingfilm.
 9. A photomask blank manufactured by the method according to claim1, wherein a content ratio ([Me]/[Cr]) between a chromium element (Cr)and a metallic element (Me) capable of bringing a mixture of themetallic element and the chromium into a liquid phase at a temperatureof 400° C. or lower is 0.7 or lower in terms of atomic ratio.
 10. Aphotomask produced by forming a pattern on the photomask blank accordingto claim
 9. 11. A method for transferring a pattern, wherein the patternis transferred to a photoresist by carrying out exposure using thephotomask according to claim 10.